The crystal structure of superconducting FeSe_1-xTe_x by pulsed neutron diffraction

A transition to a superconducting state was recently observed in the binary alloy of FeSe_1-xTe_x system where TC rises with increasing x. The substitution of the larger Te for Se ion results in no additional charges but increases the internal chemical pressure. Earlier studies suggested that the crystal structure maintains the tetragonal P4/nmm symmetry with the substitution of Te where the average bond angle, α, decreases considerably from ∼ 104° in FeSe to 100.5° in the mixed phase of FeSe _0.5Te_0.5. With the use of pulsed neutron power diffraction and the Rietveld analysis, the crystal structure refinement for FeSe _0.5Te_0.5 yielded very large thermal factors in the superconducting phase indicative of the presence of structural distortions that may be significant in understanding the electronic and magnetic properties of this system.